feat: Region PaymentProvider link (#6577)

**What**

- Introduce link between Region and PaymentProvider
- Introduce API endpoint `GET /store/regions/:id/payment-providers` for retrieving providers by region
- Add tests for both

packages/medusa/src/api-v2/store/regions/[id]/payment-providers/route.ts

@@ -0,0 +1,20 @@
+import { remoteQueryObjectFromString } from "@medusajs/utils"
+import { MedusaRequest, MedusaResponse } from "../../../../../types/routing"
+
+export const GET = async (req: MedusaRequest, res: MedusaResponse) => {
+  const remoteQuery = req.scope.resolve("remoteQuery")
+
+  const queryObject = remoteQueryObjectFromString({
+    entryPoint: "regions",
+    fields: ["payment_providers.id", "payment_providers.is_enabled"],
+    variables: {
+      id: req.params.id,
+    },
+  })
+
+  const [region] = await remoteQuery(queryObject)
+
+  res.status(200).json({
+    payment_providers: region.payment_providers.filter((pp) => pp.is_enabled),
+  })
+}

packages/medusa/src/api-v2/store/regions/middlewares.ts

@@ -24,4 +24,9 @@ export const storeRegionRoutesMiddlewares: MiddlewareRoute[] = [
       ),
     ],
   },
+  {
+    method: ["GET"],
+    matcher: "/store/regions/:id/payment-providers",
+    middlewares: [],
+  },
 ]